1. Field of the Invention
The present invention relates to electric arc welding, and more particularly, to an apparatus for pulsed arc welding and surfacing of articles.
The invention is well adapted for use in the machine-building and ship-building industries, in the aircraft-and automobile manufacturing industries, as well as in the construction industry and during repair works where welding and surfacing are carried out, utilizing consumable and non-consumable electrodes in a protective gas medium, under flux, under water, as well as in unshielded are welding and surfacing processes effected, in various spatial arrangements of electrodes.
The invention is also applicable for use in piece covered-electrode welding and surfacing, permitting various spatial arrangements of electrodes.
Applying pulses to a constant current in the process of arc welding facilitates the breaking-off of metal drops from the electrode and speeds up transfer of said drops to the welding bath.
2. Description of the Prior Art
There are known in the art apparatus for pulsed arc welding and surfacing of articles, wherein consumable, non-consumable and piece covered electrodes are utilized.
The apparatus of this type generally comprises a constant-current source and a single-pole pulse generator, functioning basically as a welding current modulator.
With the above apparatus, fusion of the electrode metal until formation of a metal drop and its transfer to the welding pool proceeds continuously for the electrode fusion is caused by the constant current.
However, as a result of burning-out of the electrode components, which is characteristic of the above process, the strength of the weld lowers, which occurs in particular in the case of welding articles made from aluminium-magnesium alloys, more than 2 mm in thickness. USSR Inventor's Certificate No. 256,134 describes an apparatus for pulsed arc welding, which comprises a power circuit, a welding current pulse shaper and a power circuit control unit. The power circuit of the apparatus includes a leakage voltage regulated three-phase step-down transformer. The transformer has its primary winding connected to a power supply. The voltage produced by the secondary winding is rectified by a main rectifier which is a multi-phase fullwave bridge rectifier. The rectifier has its positive output connected through a choke to an electrode, its negative output being electrically connected to an article being treated.
The welding current pulse shaper comprises discharge capacitors placed in circuit of each phase of the three-phase transformer, an additional rectifier coupled to an additional winding of the transformer and having controlled rectifiers or diodes and diodes. The discharge capacitors are connected in parallel through the controlled rectifiers with the main rectifier and a choke. The control unit includes static phase shifters, pulse transformers and circuit breakers. The phase shifters are connected through the pulse transformers and circuit breakers to control electrodes of the controlled rectifiers.
When the transformer is energized, the discharge capacitors are charged through the controlled rectifier to the peak voltage built up in the additional winding of the three-phase transformer. The capacitors are charged alternately during the positive half-period of the supply voltage, during which time the controlled rectifiers remain non-conductive. During the voltage negative half-periods the controlled rectifiers are alternately conducting and the capacitors discharge to feed the welding arc. As a result, high-power single-pole current pulses are formed. In the above apparatus, the controlled rectifiers are controlled by the static phase shifters. The current pulse parameters and pulse frequency may be preset automatically by a program controlling element.
However, with the use of the above-described apparatus, the electrode metal and the metal of the welding bath are acted upon by a current which causes their overheating and partial burning-out of their components, which results in a low-quality weld.
Moreover, to effect pulsed arc welding by the above apparatus, an additional rectifier is needed apart from the main one. The presence of the welding current pulse shaper including the additional rectifier complicates the welding equipment, increases production costs and requires additional production space.
It should also be noted that blocking the main rectifier by the welding current pulse shaper connected in parallel therewith results in a low stability of arcing when welding articles having a thickness less than 2 mm.